In western-style communities, colorectal cancer is the third most common form of cancer and has the second highest death rate. Over 80% of colorectal cancers originate as a polyp, which, unless there has been a family history of colon cancer, tend not to develop until the patient reaches 50 years of age. Removal of the polyp will terminate the risk of cancer originating at that site. The development from polyp to cancer is slow, usually requiring about ten years. Because of these factors, adequate screening of the “at-risk” population for colorectal cancer will have a major effect on prevention.
Techniques exist at present that can locate colonic polyps with high accuracy. Amongst the most widely used method of detection is radiological examination. However, radiological examinations of soft-tissues, such as the colon, are limited by their poor X-ray absorption characteristics. Without artificial enhancement, such tissues are poorly imaged, and a contrast agent, which strongly interacts with X-rays, such as barium sulfate, is required.
The most commonly employed radiological technique is the double contrast barium enema. This requires a strictly regulated diet, together with the administration of extremely potent laxative products, for up to 48 hours prior to the examination to produce the so-called “fully prepared colon”. Barium sulfate is then placed in the patient's rectum and colon via the anus prior to radiological examination. The barium enema examination typically carries some stigma, is uncomfortable, and word of mouth accounts usually ensure that a patient presenting for the first time already has an extensive knowledge of the unpleasantness that lies in store.
Colonoscopy is a popular, if more expensive, alternative to the barium enema but which still requires a strict dietary and laxative regime similar to the barium enema to produce the fully prepared colon. Colonoscopy requires that the patient be heavily sedated during the procedure as it is substantially more uncomfortable and invasive than a barium enema. It also entails substantially more expense to the community, and inconvenience to the patient, who may require hospitalisation. Colonoscopy also has a fairly high risk of patient injury, about 1 in 7000 patients suffering a perforation of the colon and about 1 in 50,000 dying from the procedure as a result of complications to the perforation or adverse reactions to the anaesthetic.
An alternative diagnostic technique has been introduced that is far less problematic for the patient and should increase the likelihood of acceptance by the general public. This technique has a variety of names, including Virtual Colonoscopy, Virtual Colography, CT Colography and CT Colonography. It requires the patient to undergo a CT scan of the abdomen. Subsequent image reconstruction allows examination of the colon in order to detect polyps. This technique has only become possible with the recent arrival of helical CT scanners, in which the data acquisition takes place in a continuous process (unlike previous scanners which acquired data in consecutive slices), together with high performance work stations capable of rapidly rendering 3D-views into useful medical information.
A number of trials have confirmed the feasibility of CT Colography as an accurate screening technique for colon cancer. However, this too has similar drawbacks to the other methods which may prevent it being widely used as a preventative tool against colon cancer.
Under normal circumstances the colon is heavily loaded with stool (faeces) at various stages of development. Faeces often has the same size and appearance as polyps in a CT scan, and in practical terms they are generally indistinguishable from each other.
Thus, to be effective, CT Colography requires patients to have a fully prepared colon by submitting to the same rigorous diet and laxative program used for Colonoscopy. Thus, while some of the discomfort and inconvenience of the previous procedures have been avoided, the requirement for a prepared colon has not minimised patient discomfort to the point that it will obtain high acceptance by the “at risk” population group.
The degree of discomfort and inconvenience of all the investigative techniques available to check for colonic polyps means that very much less than 10% of the “at risk” population have these examinations even once in their life, let alone at the five yearly frequencies advocated by various studies.
The above discussion of prior art is not to be construed as an admission with regard to the common general knowledge in Australia.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or at least to provide a useful alternative.